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Introduction:
The August 17th issue of the journal Science carries two high-profile papers from the RAPID
programme, analysing the first batch of data recovered from our 26N Atlantic Ocean moorings:
Kanzow et al.,
(2007) and Cunningham et al., (2007). This briefing
page aims to give an overview of these findings.
Which data do these studies use?
The anlayses use the first full-year's data (April 2004 to April 2005) recovered from the RAPID Atlantic
26N line of moorings. These data are used in conjunction with cable voltage measurements, and
satellite data, to generate a daily timeseries of "Atlantic Meridional Overturning" (or AMOC) strength. It
is the AMOC system which results in the Atlantic Heat Conveyor, moderating the climate of NW
Europe, and which most climate models suggest will weaken as a result of global warming.
What are the main findings from these studies?
Kanzow et al., 2007:
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show how the different flow components of the AMOC are related to each other
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assess and confirm the validity of the monitoring approach used
by the RAPID team to diagnose the AMOC strength
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these results allow us to place confidence in the AMOC strength
time series being accumulated by the AMOC Monitoring team
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show how the density-driven part of the AMOC varies substantially on a monthly basis
Cunningham et al., 2007:
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calculated the annual mean daily AMOC strength from April 2004 to April 2005 to be 18.7Sv (1Sv =
106m3 flow of water per second)
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established that this annual mean of daily strengths can be measured to within
1.5Sv
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report a standard deviation (indicating the day-to-day variability of strength around this annual mean) of 5.6Sv
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report a range of AMOC strength throught the time period from 4.4Sv (Feb. 2005) to 35.3Sv (Spt. 2004)
What are the implications of these findings?
The range of daily AMOC strengths (and how they are distributed through time) reported by Cunningham et al., 2007 envelopes the 5
ship-based observations
of AMOC strength reported by Bryden et al., 2005. This suggests that the long-term trend identified using these 5
ship-based observations may be an artefact of the natural variability of the system. However, to address this
possibility further we need a longer time series, and further statistical tests. The validation of the RAPID AMOC
monitoring approach, and the calculated accuracy of the technique, is an especially encouraging result - confirming that
as the time series is extended, we will be better placed to understand the natural variability
of the system and to detect any long-term trends that may be underway.
The data will also be very useful in verifying ocean and climate models simulating the AMOC and in providing a realistic
starting point for model-based projections of the AMOC.
Can I access the data used in these analyses?
Requests for access to the RAPID observational data used in the analyses should be addressed to the British Oceanographic Data Centre
(BODC).
Please refer to the Data Delivery web page at BODC for more
information.
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